pure tone audiometry spa 4302 summer 2007. the pure-tone audiometer electronic device that generates...
TRANSCRIPT
The Pure-Tone Audiometer
• Electronic device that generates tones for determining _________________
• Manufactured to specifications of the American National Standards Institute (ANSI)
• Air/Bone Conduction
• Testable frequencies (A/C): 125, 250, 500, 750, 1000, 1500, 2000, 3000, 4000, 6000, 8000 Hz
• Testable frequencies (B/C): ___ through _____ Hz
• Masking control available
Test Environment
• Background noise may affect audiometric results by __________ thresholds
• Three ways room noise may be ___________
• Earphone enclosure device
• Insert earphones – foam tipped receivers that are inserted directly into the ears
• ______________________
The Patient’s Role
• Patients must be aware that they are to indicate when they hear a tone
• Patient response: hand raise, finger raise, signal button, vocal response, play
• False responses– False negatives: patient _______________________
__________; misunderstood or forgotten instructions, feigning or exaggerating loss
– False positives: patients responds when _______________________ – usually occurs when there are long silent periods in the test
The Clinician’s Role
• Convey task instructions to patient
• Ensure understanding
• Patient position– ____________________________________________
____________________________________________
Air-Conduction Audiometry
• Specifies ______________ at various frequencies
• Can’t tell whether deficit is conductive or sensorineural, or mixed
• Earphone placed with diaphragm aimed directly over ____________
• Be careful of canals that collapse due to the pressure of the earphones – use ______________ if this is a potential problem
Air-Conduction Audiometry
• Test the known or suspected ___________ first
• Begin at 1000 Hz – easily heard by most and high test-retest reliability
ORDER of FREQS: 1000, 2000, 4000, 8000,
recheck of 1000, 500, then 250
• Test at the octave points and the mid-octaves (750, 1500, 3000, 6000 Hz) if there is a difference of 20 dB or more between adjacent octaves
Measuring a Threshold at Each Freq.
• Start presenting pure tones at ________ HL– No response? Raise the level to 50 dB HL– Still no response? Raise the level in 10 dB increments
• Whenever person responds, _____________ dB
• Whenever no response, ________________ dB
• Threshold=the lowest level at which the patient can correctly identify the tone presentation at least 50% of the time, with a minimum of 3 responses at a given level.
Air-Conduction Audiometry
• The Audiogram– Frequency (in hertz) on the x-axis, Intensity (in dB
HL) on the y-axis– Moving left to right, frequency increases; moving top
to bottom, intensity increases– Symbols are placed to correspond to threshold at a
given frequency:
Air conduction Bone conduction Air—Masked Bone—Masked
Right O < [Left X > ]
Air-Conduction Audiometry
• Pure-tone average (PTA)=average of air conduction thresholds obtained at ___, _____, and _____ Hz in one ear– Useful for predicting threshold for speech
• Percentage of Hearing Impairment– Ignores audiometric configuration and looks only at
average hearing loss– Often confusing and misleading to patients
Air-Conduction Audiometry
PTA (dB) Degree of Communication Impact
0-15 None
16-25 Slight
26-40 _______
41-55 Moderate
56-70 Moderately Severe
71-90 ______
> 91 Profound
Bone-Conduction Audiometry
• 3 Mechanisms of Bone Conduction– _______________ Bone Conduction– ____________ Bone Conduction– ______________ Bone Conduction
• Bone Oscillator Placement___________,
or, _________
Bone-Conduction Audiometry
• Occlusion Effect– When the ears of patients with normal hearing or SNHL are
covered or occluded, there is an _________ in intensity of sound delivered via a bone oscillator
– Affects ________ Hz and below– Result of increase in SPL in the ear canal when the
outer ear is covered– Markedly decreased when insert phones are used (as
opposed to supra-aural headphones)
Bone-Conduction Audiometry
• No matter where the oscillator is placed, you can never be sure which cochlea is being stimulated! (more on this to come)
• Frequencies usually tested:– 250, 500, 1000, 2000, and 4000 Hz
• Symbols for bone conduction are only connected on the audiogram (with dashed lines) when there is a __________ or __________ loss.
Audiogram Interpretation
Look at:
• hearing sensitivity by AC
• hearing sensitivity by BC
• AC/BC difference (a.k.a. the air-bone gap)
No air-bone gap = ________________
AC worse than BC = ______________ hearing loss
• Watchout: low frequencies at high levels via BC can be perceived as a __________ signal!
Another Thing to Watch Out For:• Cross Hearing: sound delivered to one ear but
perceived in the other ear.• Interaural Attenuation (IA)—How much sound it
takes to reach the other side:– Air conduction IA = __ dB– Bone conduction IA = __ dB
• Danger for cross-hearing– For AC—If AC threshold in the test ear, minus IA, is
greater than or equal to the BC threshold of the opposite ear
– For BC—If Air-bone gap of test ear exceeds ___ dB
Masking• Masking—keeping the non-test ear “busy” in order
to ensure that it is actually the test ear which is responding
• Noises used to mask:– ____________—has approximately equal energy per cycle &
covers a broad range of frequencies– _____________—made up of frequencies that immediately
surround the pure tone being tested
• Insert earphones recommended because:– They lessen the ____________– They provide much more __________________
Effective Masking: Calibration of the noise
• dB EM (Effective Masking) describes the level to which a threshold will shift in the presence of a given level of noise
• So, 45 dB EM should raise the threshold for a tone to 45 dB HL in the ear in which both are presented.
Masking
• Masking for air conduction– “Shotgun” Approach– Minimum-noise method– Maximum-noise method– ____________ method
• Masking for bone conduction– Similar to air conduction– Beware of _____________, and ___________